Catheters are flexible medical instruments for use in the introduction and withdrawal of fluids to and from body cavities, ducts, and vessels. Catheters are utilized in many different applications within the human body, including the administration of liquid therapeutic agents and the removal of bodily fluids for testing, monitoring, or disposal.
For example, catheters are used in hemodialysis procedures, in which blood is withdrawn from a blood vessel, directed to a hemodialysis unit for dialysis or purification, and subsequently returned to the blood vessel. Hemodialysis catheters can define an arterial lumen and a venous lumen. Blood is withdrawn from the patient through the arterial lumen and delivered to a dialyzer. Treated blood is returned to the patient, from the dialyzer, through the venous lumen. Positional occlusion can occur as a result of distal openings at the catheter tip being pressed against a vessel wall.